Vintage Synth Repair

I've got a broken 'd' key on my trident and want to take it off so I can repair it (or replace if I get another one). 

I can pull the key backwards but the hook on the underside of the key doesn't seem to pull back far enough to get released. I've been gentle with it so far as I don't want to make things worse.

Has anyone got any tips on getting the keys off a Korg Trident.

I've took keys off many keyboards in the past (Ensonique, yamaha and roland) but this looks a bit trickier than those ... thanks